Boyd’s Bible Dictionary:
(attire). A head-dress (Isa. 3:18; Ezek. 24:17,23); but the original implies any round ornament, as a necklace, worn by persons or animals (Judg. 8:21,26).
Concise Bible Dictionary:
An ornamental head-dress (Ezek. 24:17, 23). The same Hebrew word, peer, is translated “bonnet” (Isa. 3:20; Ezek. 44:18), and “ornament” (Isa. 61:10). In Isaiah 3:18, “round tires like the moon” is a translation of a different word, saharonim, meaning “crescents,” as in RV.